I'm looking into purchasing a bike computer, primarily to track distance and speed. Is it worth it to go up a notch and get a computer that also tracks cadence? How accurate are bike computers at doing this? I'm not interested in wireless computers - I hear too much about interference, and they are much more expensive (thus targets for thieves) -- so is it worth it to hook up more cables to the bike in order to get cadence info?

I suspect you'd get more useful answers if you asked "what are the benefits of measuring cadence" but then you'd risk duplicating this question
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MσᶎJun 26 '14 at 2:00

Re wireless, I tried a Cateye unit (one with a combined pickup) and found it very difficult to set up & keep working, radio-wise. And last week I discovered that if I turned my small LED headlight on to "flash" mode it totally disrupted the wireless speed pickup of my current unit. (The cadence pickup, oddly, is wired and was not affected.)
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Daniel R HicksJun 26 '14 at 11:37

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Wireless has come a long way. Other than yet another battery to replace, I've had zero problems with my Garmin cadence units.
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Fred the Magic Wonder DogJun 26 '14 at 14:47

Note that an alternative to measuring cadence would be to count cadence -- just produce a beep timed at what you think your ideal cadence should be, and synch your pedals to that. After all, your goal is to train yourself to maintaining a steady rate, not to measure how unsteady your rate might currently be... and a metronome beep is cheap, easy, and doesn't require any sensors on the bike.
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keshlamJun 29 '14 at 4:13

That brings up the question of what the best (Android) software is to use in place of a dedicated bike computer... given that I can get a smartphone for about the same price range. I presume that product recommendation is out of scope for us here...?
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keshlamJun 29 '14 at 23:34

5 Answers
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You're correct that there is extra cost and hassle involved in collecting cadence. The question you need to answer for yourself is: does the benefit outweigh the cost. Since you don't seem to see any benefits, the answer is obviously no.

You should buy things when they fill a need, rather than buying things because they are available.

As far as accuracy goes, they're all accurate enough as makes no difference. Modern electronics can easily generate clocks accurate to parts per million and your variation in pedalling speed is much greater than that.

It depends on the unit. Cadence is good to have, if you want to do any sort of training, but cadence is often poorly implemented. In fact, I'm not aware of ANY good computers with cadence at present. The old Cateye Micro was excellent, but it's not been available for 15 years or so.

If you get a unit with cadence you want to be sure it has a SEPARATE cadence pickup, not a combined pickup for both cadence and rear wheel speed. (The current Cateyes use a combined pickup that is impossible to keep aligned.)

As to "extra hassle", the cadence pickup, being near the crank and the foot, is slightly more apt to be knocked out of alignment than the speed pickup, but it's really not that much of a "hassle" (so long as it's not combined with the speed pickup). The main reason for not having a cadence unit is that there aren't many good ones (if any at all).

(I was making use of cadence on my bike trip last week, to help me keep my RPMs up when I got tired. It was a definite asset in that case.)

What was it about the Cateye Micro that it gave excellent cadence, and how do all current cadence measurements fall short of that? For what purposes does one need Cateye-level cadence accuracy that one cannot achieve with other levels of accuracy?
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R. ChungJun 28 '14 at 15:40

@R.Chung - It's not a matter of accuracy. The Micro was reliable and durable and not too fussy about setup. The Micro also allowed you to display cadence, speed, and distance all at once, which I've not seen on any recent units.
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Daniel R HicksJun 28 '14 at 16:04

I also think the answer is "it depends", but for slightly different reasons to Daniel. I think it depends on why you're cycling.

If you are training, then measuring cadence can definitely be useful. In fact, there are training programmes that are based around cadence. (You're basically looking for a high value, and a steady value.)

Otherwise, the information has more-or-less interest value only, although you could still argue that the "steady" side of the value could be used just to improve your technique.

As regards accuracy, cadence is measured using a magnet, just like speed and distance. So there's no reason why cadence should be any less accurate than speed and distance. It depends on the hardware of course but I'd expect computers these days to be pretty accurate.

As regards your reservations regarding wireless technology, again its going to depend on hardware but wireless is the way all the high-end computers have gone, so there is certainly not any inherent problem with this technology. It is possible to measure things like speed, cadence, power and heart rate, even I believe gearing info, all simultaneously, all wirelessly and without interference.

I use cadence all the time. It's the primary information I use on a bike computer while I'm riding.

My speed? As fast as it should be for the grade, wind, and my condition.

My distance? Not home yet.

The efficiency of my muscles and mechanical structure through the knees? That's cadence for me. I know that between 90 and 100 rpm is my personal sweet spot. Lower and I'm wasting energy by forcing too much. Higher and I'm wasting energy by spinning too much. But that's me, my body, and what I get OCD about when I should be enjoying the ride. You may be different.

Accuracy:

Accuracy is just fine. Awesome in fact. 99% of the time I'm using my Shimano Flight Deck, which does it the "poorly implemented" way, as Dan says (I think).

This means that it takes my wheel speed and my gear ratio (Flight Deck is shifter integrated), does a little math, and gives me the number that would be my cadence if I were pushing bike forward via turning the pedals.

I know when I'm coasting, so I know when the number is above reality, and I don't much care since I'm not putting meaningful power in while coasting or coast-pedaling.

Bonus: I know what cadence I will need to do when I start pedaling, so I can pre-select a gear that'll put me in my sweet spot.

I'm also using a Garmin now that has a crank sensor so it calculates it the right way. Still, the biggest number on the screen is always my cadence. Both screens.

Wireless:

Don't worry about interference. Never experienced it. Even in road race bunches and group rides. Never had a problem establishing and keeping wireless connections.

This in over a decade using Specialized and Shimano bike computers, and now a couple years on a Garmin using ANT+. Pretty sure the old Polar coded HRM never had trouble either that couldn't be explained away by my chest hair being a bigger source of interference than the wireless.

Wired computer cables can break. I may be paranoid there since I've avoided them for longer than I used them (and I did use them for a while).

I always remove computers and lights before locking a bike (I am certainly paranoid there), but have never worried about somebody wanting to steal the mounts and sensors. Just don't park by the jr high. There's always some jerk there who just wants to break other people's stuff and won't care how cheap it is to fix.

Summary: I used it a lot for a while getting started. Now I never look at it.

Cadence was one of the primary features I was looking for when getting a computer for my road bike. I bought one of the nice Bontrager wireless models where the speed sensor and cadence sensor are all in one piece on the left chainstay. (not advocating wireless, it's just what I have).

I found it to be absolutely essential when I first started riding road. I'm tall and have strong legs so on a MTB I'm a "masher". When I moved over to the road I had a tendency to pedal far too slow. I'd constantly need to look at my cadence to remember to bump it up. 80-90 on flat, 100ish up hills.

After a few hundred miles, I got very used to those rhythms, and I'm able to stay in my target areas without the counter. I'll check from time to time, out of curiosity, but I find I almost never use it any more.

So, If decide if you think you'd be the same way. Maybe use one for a bit and remove it later, or borrow one for a while.